The present invention relates to a parallel hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor/generator as a propelling power source, and specifically to such a parallel hybrid vehicle which is capable of producing a driving torque by means of at least one of the engine and the motor/generator by transmitting a combined torque of an output torque produced from the engine and an output torque produced from the motor/generator via a torque composition mechanism having a planetary gear mechanism to a transmission.
In recent years, there have been proposed and developed various parallel hybrid vehicles. One such parallel hybrid vehicle has been disclosed in Japanese Patent Provisional Publication No. 10-304513. In the parallel hybrid vehicle disclosed in the Japanese Patent Provisional Publication No. 10-304513, torque output produced from an internal combustion engine and torque output produced from a motor generator are combined into a combined torque output by means of a torque composition mechanism having a planetary gear mechanism or a planetary geartrain. The combined torque output is transmitted via a transmission to drive wheels. During early stages of the starting period of such a parallel hybrid vehicle, the parallel hybrid system usually operates to produce torque output by the motor/generator in a manner so as to bring the motor/generator speed closer to the engine speed, while suppressing a rise in the engine speed. As soon as the motor/generator speed reaches a value substantially corresponding to the engine speed, the engine and the electric motor/generator are directly coupled with each other via a direct-coupling clutch. After this, except for a drop in the vehicle speed, the parallel hybrid system operates to produce driving force (driving torque) by only the engine or by both the engine and the motor/generator. Generally, the torque output of the motor/generator is controlled or regulated responsively to a throttle opening of a throttle valve as well as engine speed. That is to say, engine torque output generated by the engine is estimated by the throttle opening and engine speed. In order to achieve the estimated engine torque, the rotational speed and torque output of the motor/generator are automatically controlled. For example, when an electronic control unit incorporated in the parallel hybrid system determines the hybrid vehicle is in a starting state, the parallel hybrid system sets the engine speed to a desired speed, and then outputs a signal indicative of the difference between the actual engine speed and the desired speed to a PID controller (i.e., a proportional-plus-integral-plus-derivative controller). The output signal value of the PID controller is used as a torque command signal value for the motor/generator, and thus the engine speed is brought closer to the desired speed by way of feedback control.
The previously-noted parallel hybrid vehicle employing a torque composition mechanism having a planetary gear mechanism, has a so-called torque-multiplication function which is realized by a ratio of the number of teeth of a sun gear to the number of teeth of a ring gear. The torque-multiplication function based on the gear ratio of sun gear to ring gear eliminates the necessity of a torque converter which is generally disposed in a power train. However, if a fluid coupling such as a torque converter does not exist in a power train, there is an increased tendency for undesired torsional vibrations to occur in the power train. In the presence of the fluid coupling (torque converter), fluid (oil) acts to effectively absorb such torsional vibrations. From the viewpoint of reduced powertrain vibrations, the use of a torque converter is advantageous, because of a smooth, vibrationless coupling function of the torque converter. On the other hand, from the viewpoint of fuel consumption, the torque converter is inferior to a planetary gear mechanism, because of energy loss of the fluid coupling (torque converter). Assuming that the engine speed also oscillates owing to undesired powertrain torsional vibrations, there is a possibility of undesirable hunting of the feedback control system for engine speed control. This may exert a bad influence on the motor/generator speed control and motor/generator torque control. To avoid this, it is possible to reduce a gain of the PID controller. As a matter of course, such a reduced gain causes a response delay of the motor/generator. As a result, the engine speed tends to rise, and simultaneously a required output torque value of the motor/generator may become larger. This undesiredly increases the car-battery capacity as well as the motor/generator size, thereby increasing a total weight of the system, and resulting in increased system production costs.
Accordingly, it is an object of the invention to provide a hybrid vehicle employing a parallel hybrid system, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a parallel hybrid vehicle, in which a motor/generator can be brought into direct-coupling state with respect to an internal combustion engine by quickly smoothly driving the motor/generator, while suppressing a rise in engine speed during starting of the hybrid vehicle, and which is capable of realizing down-sizing and lightening of the motor/generator and battery, and of reducing production costs of the system.
In order to accomplish the aforementioned and other objects of the present invention, a parallel hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor generator for propulsion, the parallel hybrid vehicle comprises a torque composition mechanism which combines a torque output produced by the engine and a torque output produced by the motor generator to generate a combined torque, and which is connected via a transmission in a powertrain to drive wheels to output the combined torque via the transmission to the drive wheels, a direct-coupling clutch which directly couples the engine with the motor generator, an engine-speed sensor which detects engine speed of the engine, a throttle opening sensor which detects a throttle opening of a throttle valve, a controller being connected electrically to the motor generator and the direct-coupling clutch for controlling the torque output produced by the motor generator and engagement and disengagement of the direct-coupling clutch, said controller allowing the direct-coupling clutch to operate in a disengaged state and allowing the engine speed to be maintained at a predetermined value during starting of the vehicle, the controller comprising a desired motor/generator torque setting section which sets a desired motor/generator torque on the basis of both the engine speed and the throttle opening from a predetermined characteristic map to generate a signal indicative of the desired motor/generator torque, and a response-characteristic compensation section which attenuates high-input-frequency components and passes low-input-frequency components, out of the signal indicative of the desired motor/generator torque set through the desired motor/generator torque setting section, to generate a compensated signal. The controller controls the torque output of the motor generator on the basis of a signal value of the compensated signal generated by the response-characteristic compensation section.
According to another aspect of the invention, a parallel hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor generator for propulsion, the parallel hybrid vehicle comprises a torque composition means including a differential system for combining a torque output produced by the engine and a torque output produced by the motor generator to generate a combined torque, the torque composition means connected via a transmission in a powertrain to drive wheels for outputting the combined torque via the transmission to the drive wheels, a direct-coupling clutch which directly couples the engine with the motor generator, an engine-speed sensor means for detecting engine speed of the engine, a throttle opening sensor means for detecting a throttle opening of a throttle valve, a torque control means connected electrically to the motor generator and the direct-coupling clutch for controlling the torque output produced by the motor generator and engagement and disengagement of the direct-coupling clutch, the torque control means allowing the direct-coupling clutch to operate in a disengaged state and allowing the engine speed to be maintained at a predetermined value and allowing the direct-coupling clutch to engage at a timing when the engine speed synchronizes a rotational speed of the motor generator during starting of the vehicle, the torque control means comprising a desired motor/generator torque setting means for setting a desired motor/generator torque on the basis of both the engine speed and the throttle opening from a predetermined characteristic map to generate a signal indicative of the desired motor/generator torque, and a response-characteristic compensating means for attenuating high-input-frequency components and for passing low-input-frequency components, out of the signal indicative of the desired motor/generator torque set through the desired motor/generator torque setting means, to generate a compensated signal, and the torque control means controlling the torque output of the motor generator on the basis of a signal value of the compensated signal generated by the response-characteristic compensating means.
According to a further aspect of the invention, an electronic control method for a parallel hybrid vehicle employing a parallel hybrid system, using both an internal combustion engine and an electric motor generator for propulsion and including a direct-coupling clutch directly coupling the engine with the motor generator, and an engine-braking clutch incorporated in a transmission in a powertrain, the electronic control method comprises detecting a throttle opening of a throttle valve, calculating an average throttle opening as a time mean of the throttle opening, detecting engine speed of the engine, calculating an average engine speed as a time mean of the engine speed, retrieving a desired motor/generator torque of the motor generator on the basis of the average throttle opening and the average engine speed from a predetermined characteristic map to produce a signal indicative of the desired motor/generator torque, calculating an average desired motor/generator torque as a time mean of the desired motor/generator torque, detecting a reduction ratio of the transmission in the powertrain, detecting input information regarding which state the direct-coupling clutch is in, detecting input information regarding which state the engine-braking clutch is in, selecting a response-characteristic-compensator frequency characteristic responsively to the reduction ratio of the transmission, the input information regarding which state the direct-coupling clutch is in, and the input information regarding which state the engine-braking clutch is in, making a response-characteristic compensating process of the selected response-characteristic-compensator frequency characteristic to the signal indicative of the average desired motor/generator torque to generate a compensated motor/generator torque command, and controlling the motor generator in response to the compensated motor/generator torque command. The response-characteristic-compensator frequency characteristic may be set at a higher level with a decrease in the reduction ratio of the transmission. The response-characteristic-compensator frequency characteristic may be set at a higher level in presence of a transition from an engaged state of the engine-braking clutch to a disengaged state and set a lower level in presence of a transition from the disengaged state of the engine-braking clutch to the engaged state. The response-characteristic-compensator frequency characteristic may be set at a higher level in presence of a transition from an engaged state of the direct-coupling clutch to a disengaged state and set at a lower level in presence of a transition from the disengaged state of the direct-coupling clutch to the engaged state.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.